\clist_item:Nn is expandable


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4476 de43f980-851b-0410-b2f7-c40aca1f87e0
Fix behaviour of \SplitArgument with missing items

The documented behaviour here is that missing items should give an empty argument,
but we had `\NoValue` appearing. That's  wrong, at least as far as the docs go.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4477 de43f980-851b-0410-b2f7-c40aca1f87e0